Tobacco smoke filter

ABSTRACT

Disclosed are cigarette filters containing compositions of certain cobalt or iron chelates adsorbed or supported on the surface of a suitable particulate support such as activated carbon particles. These cigarette filters remove substantial quantities of nitrogen oxides from cigarette smoke. Chelates suitable for use in this invention are of iron or cobalt and an organic compound containing a GROUP AND A FUNCTIONAL GROUP CAPABLE OF FORMING A BOND WITH THE IRON OR COBALT ATOM. In a first embodiment of the cigarette filter aspect of the invention the cigarette filter can comprise a cylinder of crimped, continuous, plasticized cellulose acetate fibers, and the activated carbon particles, having the chelate adsorbed or supported on the surface thereof, are bonded to the cellulose acetate fibers. In a second embodiment of the cigarette filter aspect of the invention the cigarette filter can comprise a first cylinder of crimped, continuous, plasticized cellulose acetate fiber, and coaxially positioned with respect to the first cylinder, a second cylinder of a composition comprising the activated carbon particles having the chelate adsorbed or supported on the surface thereof. In the composition aspect of the invention the composition comprises the material used to prepare the second cylinder. In one aspect of this invention the functional group capable of forming a bond with the iron or cobalt atom can be -OH or The chelate of cobalt and the condensation product of salicylaldehyde and ethylene diamine is a particularly desirable chelate for use in this invention. Polyethylene glycol diacetate is a particularly desirable plasticizer for the cellulose acetate fibers because it can also be used for bonding the activated carbon particles to the cellulose acetate fibers.

United States Patent 1 Reynolds et al.

54] TOBACCO SMOKE FILTER [75] Inventors: Jefferson W. Reynolds; CephasH.

Sloan, both of Kingsport, Tenn.

73 Assignee: Eastman Kodak Company, Rochester, NY.

[22] Filed: Sept. 23, 1971 [21] Appl.No.: 183,223

[52] US. Cl. ..131/266, 131/262, 131/10.7 [51] Int. Cl. ..A24b 15/02[58] Field of Search...260l566 R; 252/431; 131/10.7,

[56] References Cited UNITED STATES PATENTS 3,280,823 10/1966 Bavley eta1. ..131/262 A 3,319,635 5/1967 Stahly ..13/262 R 3,460,543 8/1969Keith et a1. ...13 l/266 X 2,815,730 12/1957 Schreus et al. ..131/262 APrimary Examiner-Melvin D. Rein Att0rney-Cecil D. Quillen, Jr.

[57] ABSTRACT Disclosed are cigarette filters containing compositions ofcertain cobalt or iron chelates adsorbed or supported on the surface ofa suitable particulate support such as activated carbon particles. Thesecigarette filters remove substantial guantities of nitrogen o sides fromcigarette smoke. Chelates suitable for use in this [111 3,724,469 [451Apr. 3,1973

invention are of iron or cobalt and an organic corn pound containing agroup and a functional group capable of forming a bond with the iron orcobalt atom. In a first embodiment of the cigarette filter aspect. ofthe invention the cigarette filter can comprise a cylinder of crimped,continuous, plasticized cellulose acetate fibers, and the activatedcarbon particles, having the chelate adsorbed or supported on thesurface thereof, are bonded to the cellulose acetate fibers. In a secondem- I bodiment of the cigarette filter aspect of the invention groupcapable of forming a bond with the iron or cobalt atom can be -OH or Thechelate of cobalt and the condensation product of salicylaldehyde andethylene diamine is a particularly desirable chelate for use in thisinvention. Polyethylene glycol diacetate is a particularly desirableplasticizer for the cellulose acetate fibers because it can also be usedfor bonding the activated carbon particles to the cellulose acetatefiibers.

5 Claims, No Drawings TOBACCO SMOKE FILTER This invention relates to theselective removal of nitrogen oxides from cigarette smoke by means of afilter comprising a suitable particulate support, such as activatedcarbon particles and, adsorbed or supported on the surface of theparticles, a chelate of iron or cobalt and an organic compoundcontaining group and a functional group capable of forming a bondbetween the iron or cobalt atom.

Cigarette smoke filters that remove nitrogen oxides from cigarette smokeare reported in US. Pat. Nos. 3,327,718; 3,407,820 and 3,434,479.

The irreversible reaction between nitric oxide andN,N'-ethylenebis(salicylideneiminato) cobalt as well as otherSchiff-base complexes of cobalt are described in the followingreferences: (1) F. Rallo and P. Silvestroni, Ricerca Sci. Rend., Sez. A3 (7), 1001-6 (1963), Chem. Abstr., 60, 7668 (1964); (2) A. Earnshaw, P.C. Hewlett, and L. F. Larkworthy, J. Chem. S.oc., 1965, 4718-23; and (3)H. Diehl and C. C. Hach, Inorganic Synthesis, 3, 196 (1950). No mentionismade of the use of these cobalt chelates on a support such asactivated carbon which allows an extremely fast reaction to occurbetween the complexes and these oxides of nitrogen.

Phthalocyanine complexes of iron and cobalt are cited in the literatureas capable of reacting with the Here again no mention is made ofsupporting the complexes or their use as a cigarette filter additive toselectively remove the oxides of nitrogen from' cigarette smoke.

In broad summary this invention relates both to cigarette filters whichremove substantial quantities of nitrogen oxides from cigarette smokeand also to compositions used in preparing these filters.

In a first embodiment of the cigarette filter-aspect of r the inventionthe cigarette filter can comprise .a cylinder of crimped, continuous,plasticized cellulose acetate fibers, and the adsorbent suchas activatedcarbon particles, having a chelate adsorbed on .the surface thereof, isbonded to the cellulose acetate fibers.

In a second embodiment of the cigarette filter aspect of the inventionthe cigarette filter can comprise a first cylinder of crimped,continuous, plasticized cellulose acetate fiber and coaxially positionedwith respect to the first cylinder a second cylinder of a compositioncomprising the adsorbent such as activatedcarbon particles having thechelate adsorbed on the surface thereof.

In the composition aspect of this invention the composition comprisesthe material used to prepare the second cylinder in the secondembodiment of the cigarette filter aspect of the invention.

An advantage of this invention isithe removal of substantial quantitiesof nitrogen oxides from cigarette smoke.

group and a functional group capable of forming a chemical bond with theiron or cobalt atom. In one embodiment the functional group can be -OHor The organic compound can be aliphatic or aromatic in character.

One particularly desirable chelate is the cobalt (ll) chelate of thecondensation product of salicylaldehyde and ethylenediamine. To preparethis chelate, sometimes called salcomine," 2 moles of salicylaldehydeare condensed with one mole of ethylenediamine to produce the compound:

-HC=IIT III=CH- CHr-CH:

This compound is then reacted. with a suitable salt of cobalt, such ascobalt chloride or cobalt acetate, to

produce salcomine or N,'N'-ethylenebis(salicylideneiminato) cobalt (II)corresponding to the structure a--.

/ o=N N=OH l CH2 This method of preparing salcomine is well known in theliterature such as H. Diehl and C. C. Hoch, Inorganic Synthesis, 3.,196-201 (1950).

Other iron and cobalt chelates suitable for use in this invention can beprepared according to procedures well known in the art. Examples ofother chelates are:

l. Cobalt chelated with the reaction product of 5- chlorosalicylaldehydeand ethylenediamine gives N,N'-

ethylenebis( 5-chloro-2-forminidoylphenolato) cobalt.

2. Cobalt chelated with the reaction product of salicyladehyde and1,2-propane diamine gives,N,N'- propylene bis(o-formimidoylphenolato)cobalt.

3. Cobalt chelated with the reaction product of salicylaldehyde ando-phenylenediamine gives -N,N'-ophenylene bis(o-formimidoylphenolato)cobalt.

4. Cobalt chelated with the reaction product of salicylaldehyde and3,3'-diaminodipropylamine gives N,N'-.(.2,2'-iminodiethylene)bis(o-formimidoylphenolato) cobalt in which there are three coordinatebonds to nitrogen atoms.

5. Cobalt chelated with the reaction product of acetylacetone andethylene diamine gives the structure below which is N,N-ethylenebis(3-acetimidoyl-2- propen-2-ato) cobalt.

6. Cobalt chelatedwith phthalocyanine gave a compound of the structureThe activated carbon particles can have a U. S. Standard Sieve size of14-50, an area of 500-1250 m /gm and a pore volume of 0.5-9.5 ml/gm. Inanother aspect of the invention the activated carbon particles can havean area of 900-1200 m /gm, and a pore volume of 0.6-0.95 ml/gm.

Examples of suitable activated carbons useful in this invention are 1.National Carbon Co. Type CXC from Petroleum, 500 MF/g. area, 0.6 ml./g.pore volume and 0.5 percent ash.

2. Pittsburgh Type BPL from bituminous coal, 1050-1150 M./g. area, 0.80ml./g. pore volume and 2 percent ash.

3. Pittsburgh Type CAL from bituminous coal,

1000-1100 MF/g. area, 0.94 ml./g. pore volume, and

All of these activated carbons are completely permeated by systems oflarge macropores and appreciable concentrations of pores with 30 Adiameters. Types CAL, CPG, L and SGL have appreciable concentrations ofpores with 30-1000 A diameters.

Other supports that can be used include:

1. Davision Grade 70 silica, 300 M.'/g. area and 1.22 mL/g. pore volume.

2. Alcoa Grade F-l alumina, 210 M. /g. area and about 0.4 ml./g. porevolume.

3. Harshaw Grade Al-0l04 alumina, M. /g. area and about 0.4 ml./g. porevolume.

4. Iron III oxide prepared in the laboratory, about 250 M./g. area and0.3 ml./g. pore volume.

5. Charles Loeb Pipes, Inc. meerschaum, 280 MF/g. area and 1.4 ml./g.pore volume.

6. Rohm and Haas XAD-7, a polymethacrylate resin, about 30 mesh spheres,400 Mfilg. area and about 0.6 ml./g. pore volume.

In the first embodiment of the cigarette filter aspect of thisinvention, the cigarette filter comprises a cylinder of crimped,continuous plasticized cellulose acetate fibers and the activatedcharcoal particles, having the chelate adsorbed on the surface thereof,are bonded to the cellulose acetate fibers. In this embodiment theactivated carbon particles can be bonded to the cellulose acetate fibersby using plasticizers well known in the art. One particularly desirableplasticizer that can be used is polyethylene glycol diacetate whereinthe polyethylene glycol has a molecular weight of 600-800.

Polyethylene lycol diacetate can be prepared by reacting aceticanhydride with polyethylene glycol, and distilling off the acetic acid.Polyethylene glycol diacetate is particularly desirable for use to bondthe crimped, continuous cellulose acetate fibers into a firm cylindricalrod suitable for preparation into cigarette filters because thepolyethylene glycol diacetate can also be used to bond the activatedcarbon particles to the cellulose acetate fiber. The polyethylene glycoldiacetate is also desirable for use because in contrast to many othermaterials the polyethylene glycol diacetate does not substantiallyreduce the effectiveness of the activated charcoal to remove undesirablecomponents other than nitrogen oxides from cigarette smoke. Thepolyethylene glycol diacetate can contain about 4 percent by weightcellulose acetate if desired.

In the first embodiment of the invention the activated carbon or othersupport having the chelate on the surface thereof can, according tomethods well known in the art, be dusted or shaken onto a spread band ofcellulose acetate cigarette filter tow which is then plasticized andfurther processed into a cylindrical rod of the same circumference asthat of a cigarette. The filter rod can then be wrapped with paper andcut into any desired length. The finished filter can then be mounted onthe cigarette according to conventional methods.

In a second embodiment of the cigarette filter aspect of the invention,the filter can comprise a first cylinder of crimped, continuous,plasticized cellulose acetate fiber and, coaxially positioned withrespect to the first cylinder, a second cylinder of activated carbonparticles having the chelate adsorbed on the surface thereof.

In a variation of this embodiment the filter can also comprise a thirdcylinder of plasticized cellulose acetate fibers, the third cylinderbeing coaxially positioned with respect to the first and secondcylinders and disposed so as to position the second cylinder between thefirst and third cylinders.

According to this invention the cellulose acetate fibers can be fromabout 0.1-50 denier and have an acetyl content of 38-40. Inone preferredembodiment 3.3 denier filaments of 39.8 percent acetyl content are used.Of course other filter elements such as baffles, paper,- etc. can beused in conjunction with either the first or second embodiment of thecigarette filter aspect of the invention.

In the following examples selective filtration tests were conducted byusing an automatic syringe-type smoking machine taking a 35 ml. puff of2 sec. duration once each minute. Usually puffs were required to reachthe desired 27 mm. butt length of the used cigarette. Puffed cigarettesmoke was first passed through a Cambridge (Type CM-113A) filter toremove tar and nicotine and then into an evacuated collection bottlecontaining reagent for the colormetric analysis of the oxides ofnitrogen. [Saltzman, J. Anal. Chem. 26, 1949 (1951)]. Filter additivesweretested in duplicate and compared with three control filters whichcontained nonactivated carbon.

EXAMPLE 1 The Type CXC carbon described above was used to prepare afilter additive containing 5 percent of salcomine. Two 0.2 ml. portionsof the granular additive were tested in three-component acetate filters.To prepare the additive 6.21 g. of the carbon was impregnated with 0.33g. of the cobalt compound in 12 ml. of chloroform. The mixture wasstirred and evaporated at 25C. to give dry-appearing granules which weretreated several hours at 25C. in a vacuum desiccator containing calciumchloride and 13X molecular sieve. The weight of the material was 6.78 g.and its bulk volume was 14.1 ml. Two cigarette filters were prepared asdescribed above from 0.2 ml. (0.0962 g.) portions of the additive andattached to'65 mm. long tobacco columns. These cigarettes weremachinesmoked to a 27 mm. butt length and the gas phase of the smoke wascollected in an evacuated, one liter collection bottle containing 50 ml.of the reagent for colormetric analysis. Smoke from the two cigarettescontained an average of 224 ug. of NO-N O compared to an average of 362pg. for three controls with the same type of filter containing 0.2 ml.portions of nonactivated carbon. The supported cobalt chelate additiveremoved 38 percent of the NONO from the smoke. Filters containing 100mg. of untreated CXC carbon gave higher deliveries of NO-NO; than thecontrol filter containing nonactivated carbon. This is believed to becaused by adsorption on the activated carbon of some smoke componentswhich react with a portion of the NONO to effectively remove it from thesmoke. The smoke vapors pass through the nonactivated carbon essentiallyunchanged.

EXAMPLE 2 A band of cellulose acetate filter two (3.3-den./fil., 44,000total denier) 12 inches in length was spread out and sprayed withglyceryl triacetate (bonding agent) so that it contained 8 percent byweight. Granules of the impregnated carbon additive (prepared asdescribed in Example 1) were then applied uniformly to the spreadout towuntil 31 percent additive had been added. The tow was drawn into acylindrical mold of the same inside diameter as that of a cigarette andallowed to become firm. The cured filter rod'was cut into mm. segmentsfor testing. Each 20 mm. segment contained an average of 0.1 120 gramsof additive.

pg. NO--NO, Del. NO-NO Removed Filter Through Filter From Cig. SmokeControl 351 0 Filter Cont. 245 30 Additive EXAMPLES 3 -l l Activatedcarbons (CXC, BPL, PCB) described above were impregnated with salcominefrom a chloroform solution, dried and tested in cigarette filters 'asdescribed inExample l.

Theresults are presented in Table 1.

rx'is'i'ni [NO-N02 removal by salcomine supported on activated carbon]Mierograms N O- N 02 in smoke 1 Percent Additive, Percent 02 ExampleCarbon g. (0.2 salco- Control Additive removed number type ml.) minefrom smoke CXC .0065 10 303 214 CXC 0014 5 300 208 (JXG 0022 2. 5 352302 CXC .1115 10 303 214 B lL 1006 5 352 265 B PL 1036 2. 5 352 278 CXC.0065 10 345 260 CXC .0006 5 348 208 P C B 1245 5 354 289 "Additive waswet with 0.015 gram of water per 0.2 ml. additive. "Additive stored 14days on cigarette.

EXAMPLES 12-16 Additives containing 5 percent salcomine oncertain of theactivated carbons (2.07 g.) described above were prepared byimpregnation with dimethylformamide (DMF) solutions (0.11 g. salcominein 14 ml.). Most of the DMF was removed by evaporation and stirring atC.; final treatment was at about C. and 1 mm. Hg in a vacuum tube.Removal of NONO, in cigarette smoking tests as described in Example 1 isshown in Table 2. Filter construction is for 0.2 ml. of additive.Additive volumes of 0.1 and 0.4 ml. were placed in 2.5 and 10 mm.sections of the filters.

TABLE 2 [N O-NO2 removal by salcomine supported on activated carbon]Percent Miemgrams NO- NO-NO2 Volume N 02 in smoke removed Example CarbonAddiaddifrom number type tive, g. tive, ml. Control Additive smoke CXC-0426 0. 1 351 277 21 CXC. 0851. 0. 2 355 195 44 CXC 1702 0. 4 351 76 78G P G 0468 0. 1 353 276 22 GP G 0935 0. 2 353 48 GP G 1870 0. 4 353 4886 CAL 0908 i 0. 2 353 207 41 CL .0873 0. 2 353 202 16 S GL 0060 0. 2353 35 EXAMPLES 17-22 Silica, alumina, iron [11 oxidle, meerschaum andXAD-7 supports described above wereused instead of carbon to supportsalcomine as described in Example culated) on CXC activated carbon wasprepared in a l. A different solvent, methylene chloride, was usedinstead of chloroform in Example 17. Results of smoking tests asdescribed in Example 1 on 0.2 ml. of the additives (about 0.0044 g.salcomine per 0.2 ml.) are distilled water. All but 1 g. of the waterwas evaporated to give dry-appearing granules which were impregnatedwith 4 ml. of a buffered solution (2.15 g. sodium hydroxide and 0.10 g.sodium acetate per 100 ml. of

presented in Table 3. 5 water) containing 0.0908 g. of N,N'-disal- TABLE3 [NO-NO2 Removal by salcomine on various supports] Percent MicrogramsNO--NO2 Percent NONO2 in smoke removed Example Additive, salcomine fromnumber Support material g. (0.2 m1.) onsupport Control Additive smoke 17Grade 70501021." 1000 5. 0 347 .280 10. 3 18 Alumina, F1 2025 2. 3 3502158 I 24. 0 1H. Alumina, Al0104 2523 1.8 350 322 8. 0 20. Iron 111oxide... .0605 6. 6 350 317 0. 2 21... Meerschaum 1798 2. 4 350 325 6. 922, XAD-7 resin .0014 5. 0 301) 280 .1. 0

EXAMPLES 23-27 icylalethylenediamine. After removal of the water bySalcomine or salcomine-type chelates (5 percent) were supported on TypeCPG activated carbon as described in Example 1. The results of NONOremoval from cigarette smoke in tests similar to those described inExample 1 are shown in Table 4.

TABLE 4 REMOVAL OF NO-NO FROM CIGARETTE SMOKE BY SUPPORTED COBALTCHELATES Micrograms NONO,

A filter additive, prepared from 2.07 g. of Type CXC activated carbonand 0.11 g. of salcomine (5 percent, calculated), was tested for removalof NO--NO from cigarette smoke as described in Example 1. A quantity of0.0843 g. of cobalt acetate tetrahydrate was reacted with 0.0999 g. ofN,N-disalicylalethylene diamine in 5 ml. of chloroform over a period of0.5 hr. to give a dark brown solution which was used to impregnate thecarbon. After removal of the chloroform as described in Example 1,smoking tests showed that 0.2 ml. (0.0951 g.) of the additive in afilter removed 14 percent of the NO---NO from cigarette smoke. TheNO--NO delivery was 298 pg. compared to 347 pg. for the control.

EXAMPLE 29 A filter additive containing 5 percent salcomine (caltwo-stepimpregnation process. A quantity of 2.07 g. of the carbon wasimpregnated with a solution of 0.0843

g. of cobalt acetate tetrahydrate dissolved in 3 ml. of

evaporation on a hot plate and in a vacuum desiccator over calciumchloride, 0.2 ml. (0.0901 g.) of the additive removed, 10 percent of theNO-NO from cigarette smoke in tests as described in Example 1. The NONOdelivery was 316 pg; compared to 351 pg. for the control.

EXAMPLE 30 v Type CXC activated carbon containing 5 percent salcominewas prepared as described for Examples 12-16 except dry acetic acid wasused in place of DMF as solvent for the salcomine. Tests on 0.2 ml.(0.0882 g.) of the additive as described in Example 1 showed that itremoved 35 percent of the NONO (228 pg. vs. 352 pg. for control) fromcigarette smoke.

EXAMPLE 31 A filter additive (0.2 m1., 0.0957 g.), prepared from 2.07 g.of Type CPG carbon and 0.11 g. of the cobalt chelate (5 percent,calculated) with the acetylacetoneethylene diamine Schiff base, removed16 percent of the NO-NO from cigarette smoke in tests as described inExample 1. Filters containing the additive delivered 298 pg. of NO-NOvs. 357 pg. for the controls. A brown solution of the chelate, preparedby reacting 0.0974 g. of cobalt acetate tetrahydrate with 0.0877 g. ofthe Schiffs base in 4 ml. of warm water, was used to impregnate thecarbon; water was removed by evaporation on a hot plate at C.

EXAMPLE 32 steam bath and in a vacuum desiccator containing Type 13Xmolecular sieve.

EXAMPLE 33 A filter additive (0.2 ml., 0.0980 g.) prepared in ex-- actlythe same way as the one described in Example 32 from 0.30 g. (15percent) of cobalt phthalocyanine and 1.70 g. of Type CXC carbon removed14 percent of the NONO in similar smoking tests. Deliveries of NO- Nwere 280 ug. for the additive and 326 pig. for the controls.

EXAMPLE 34 Salcomine (0.30 g.) was dissolved in ml. of.

chloroform. A portion of the solution was applied to a paper filter mm.in length. The filter was weighed before applying the solution andweighed again after the solvent had evaporated. The percentage ofsalcomine deposited on the filter was 10 percent of the total weight ofthe filter. The filter was attached to a cigarette which was thensmoked. The smoke vapors were analyzed for nitrogen oxides by the methodreferred to in Example 1. A duplicate filter was similarly analyzed.Control filters (untreated paper filters) 20 mm. in length, wereattached to cigarettes and smoked. Vapors passing through the filterswere analyzed for NONO,. None of the NO-NO was removed by thepaper-supported salcomine filters,

Smoke vapors passing through the treated filters contained 325 ug. NONOand smoke vapors passing The preferred method of preparation of thefilter ad ditive is by impregnation of a preformed support with asolution of the metal chelate and then removal of the solvent.Wet-mixing techniques might be useful in the preparation of theadditive. Chloroform, methylene chloride, pyridine, water, acetic acid,and DMF'were used successfully as solvents for the metal chelates; thereare undoubtedly others. In fact, the solvent choice may be an extremelyimportant factor in additive activity since the metal chelatescrystalline form is believed to be influenced by the solvent. The metalchelate may be prepared in the solvent (Examples 28, 31)

or in the support (Example 29).

EXAMPLE lowed to slowly perculate through this bed in order to 7 removetraces of color and minor impurities. Aclear, colorless polyethyleneglycol diacetate (approximately 3200 g.) was obtained after thistreatment.

Cellulose acetate powder (39.5 percent acetyl).was dissolved in thepolyethylene glycol diacetate. The final solution containingapproximately 4 percent cellulose acetate by weight had a viscosity ofabout 500 centistokes at 25C.

Filter rods consisting of cellulose acetate fibers, the bondingplasticizer described above, and activated carbon particles wereprepared accordingly. A cellulose acetate tow consisting of 12,000cellulose acetate fibers of 5 den./fil. and crimped to 15 crimps perinch was spread to a width of 15 in. and sprayed with polyethyleneglycol diacetate (molecular weight about 720) containing 4 percentcellulose acetate. Charcoal granules having a suitable chelate adsorbedthereon were added to the moving tow which contained 8 percent of theplasticizer mixture, and it was immediately processed into mm. filterrods. It was observed that very little charcoal fell from the movingfilter tow during processing. Moreover, the completed rods retained thecarbon, even when vigorous tapping was used in attempts to shake it fromthe rods.

The invention has been described in detail with particular reference topreferred embodiments thereof, but it will be understood that variationsand modifications can be effected within the spirit and scope of theinvention. We claim:

l. A tobacco smoke filter comprising A. a first cylinder of crimped,continuous, plasticized cellulose acetate fiber, 1 B. coaxiallypositioned with' respect to the first cylinder, a second cylinder ofactivated carbon particles having a U. S. Standard Sieve size of 14-50,an area of 500-1250 m lgm and a pore volume of 0.5-9.5 ml/gm and,adsorbed or supported on the surface thereof, a chelate of iron orcobalt and an organic compound containing a group and a functional groupcapable of forming a chemical bond with the iron or cobalt atom.

2. The filter of claim 1 wherein the activated carbon particles have anarea of 900-1200 m /gm, and a pore volume of 0.6-0.05 v

rnl/gm, and the functional group capable of forming a chemical bond withthe iron or cobalt is OH or

2. The filter of claim 1 wherein the activated carbon particles have anarea of 900-1200 m2/gm, and a pore volume of 0.6-0.05 ml/gm, and thefunctional group capable of forming a chemical bond with the iron orcobalt is -OH or
 3. The filter of claim 2 wherein the chelate is ofcobalt and an aromatic or aliphatic organic compound and the functionalgroup is -OH.
 4. The filter of claim 3 wherein the chelate is of cobaltand the condensation product of salicylaldehyde and ethylenediamine. 5.The filter of claim 4 further comprising a third cylinder of plasticizedcellulose acetate fibers, the third cylinder being coaxially positionedwith respect to the first and second cylinders and disposed so as toposition the second cylinder between the first and third cylinders.